Coexistence of ferrimagnetic long-range order and cluster superparamagnetism in Li1-xNi1+xO2 - art. no. 094437

We study numerically and analytically a simple model for the magnetic prope rties of moderately impure (x less than or equal to0.2) Li1-xNi1+xO2 compou nds. The model largely relies on available experimental results and it is i nvestigated by complementary methods: percolation and Monte Carlo simulatio ns, together with random-field analytical theory. Our results conclusively show a critical change of the magnetic response above a given concentration x(c) = 0.11-0.14. We find that. beyond this concentration, the unusual fea tures of the spontaneous magnetization observed experimentally result from the coexistence of ferrimagnetic long-range order with cluster superparamag netism.